Preheat your oven to 350°F (175°C) and line a muffin tin with cupcake liners.

In a mixing bowl, whisk together 2 cups of all-purpose flour, 2 teaspoons of baking powder, and 1/2 teaspoon of salt.

In a stand mixer, cream together 1/2 cup of softened unsalted butter and 1 cup of granulated sugar on medium speed for about 2 minutes.

Add 2 large eggs and 1 teaspoon of vanilla extract to the butter mixture, mixing until fully incorporated.

Gradually add the dry ingredients to the wet mixture, alternating with 1/2 cup of milk, mixing until just combined.

Fill each cupcake liner about 3/4 full and bake for 18-20 minutes, or until a toothpick comes out clean.

Allow the cupcakes to cool in the pan for about 5 minutes before transferring to a wire rack to cool completely.

In a saucepan over low heat, whisk together 4 egg yolks, 1 cup of sugar, zest from 2 lemons, 1/2 cup of fresh lemon juice, and a pinch of salt, stirring for 10-12 minutes until thickened.

Whisk in 4 tablespoons of butter until melted and allow the lemon curd to cool.

Beat 1/2 cup of softened unsalted butter until smooth, then gradually add 2 cups of powdered sugar and the juice of one lemon until creamy.

Once cupcakes are cool, hollow out the centers, pipe frosting around the edges, and fill each center with lemon curd.

Chill cupcakes in the refrigerator for 15-20 minutes before serving.